Unable to map httpapi to exisiting customdomain

[rockey5520]

Description:

I am trying to create a httpapi and map to an exisitng custom domain

Steps to reproduce:

Sample template.yml file

Resources:
  HttpApi:
    Type: AWS::Serverless::HttpApi
    Properties:
      StageName: !Ref StageName
      Tags:
        Tag: Value
      AccessLogSettings:
        DestinationArn: !GetAtt AccessLogs.Arn
        Format: $context.requestId
      StageVariables:
        StageVar: Value
      FailOnWarnings: True
      CorsConfiguration:
        AllowOrigins:
          - "*"
        AllowHeaders:
          - origin
          - content-type
          - x-amz-date
          - authorization
          - x-api-key
          - x-amz-security-token
        AllowMethods:
          - GET
          - POST
          - OPTIONS
          - PATCH
          - DELETE
        MaxAge: 0
      Domain:
        DomainName: x.x.x
        CertificateArn: arn
        EndpointConfiguration: REGIONAL
        Route53:
          HostedZoneId: XXXXXXXXXXX
        BasePath:
          - /banks

Observed result:

The domain name you provided already exists.    
                                                                                                                                                      (Service: AmazonApiGatewayV2; Status Code: 400; 
                                                                                                                                                      Error Code: BadRequestException; Request ID:    
                                                                                                                                                      ; Proxy:    
                                                                                                                                                      null) 

Expected result:

Map created httpapi to the custom domain and under paths given as per the template section BasePath

Additional environment details (Ex: Windows, Mac, Amazon Linux etc)

1. OS: Ubuntu
2. sam --version: 1.16.0
3. AWS region: eu-west-1

Add --debug flag to command you are running

[CoshUS]

Hey @rockey5520,
SAM always creates a AWS::ApiGatewayV2::DomainName resource if DomainName is specified.
https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/sam-specification-generated-resources-httpapi.html
To use existing custom domain, you can remove DomainName and use AWS::ApiGatewayV2::ApiMapping resource instead.
Closing. Let me know if there are other issues.

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[rockey5520]

Hey, @CoshUS I suppose your suggestion works and fits nicely for hello-world type applications. but this is not the ideal way of building mapping API to an existing domain which is already having several mappings from other API's

This approach only makes things complex by removing touching the components(API mapping, in turn downtime) during deployment. can we get this issue to be converted as a feature for sam cli?

[CoshUS]

@rockey5520 Sounds good. I'll transfer this to SAM repo and the feature request would be:
Add support for using existing custom domains for AWS::Serverless::HttpApi and AWS::Serverless::Api

[rockey5520]

@CoshUS Thank you

[hoffa]

Tangentially related request in #2778 (comment)